As far as mental health goes... Can a factor be our 40+ hour work weeks and limited time off? I feel like we work too much for the most part.
I wholly support more paid vacation time, and curtailing over time.
There's little question that would be beneficial in reducing stress; and at the same time, I think the case for productivity and economic benefits is very real as well.
That said, I'd be careful about the degree to which work-related stress is a primary cause of mental illness.
Obviously it depends on what type of mental illness one is discussing.
But aside from genetic factors; or the like, factors range widely from chemical imbalances to inadequate daylight to sleep disorders and so on.
All of these though are typically easier to handle if you have time to take a breath and reflect, talk to friends and family, or catch up on some sleep.
Robust mental healthcare and supports would surely top the list of things society can do; along with alleviating poverty, as more money tends to reduce stress and provide options for addressing one's problems.
But more vacation time or curtailing overtime is really a matter of legislation and therefore comes at relatively low-cost. We're also well below global norms, so I wouldn't expect any competitiveness issue.
The entire E.U., the U.K, Australia and NZ all mandate 4-weeks paid vacation (or more); and even Saskatchewan is at 3 weeks; and Quebec at 3 weeks after 3 years with the same employer.
While the U.S. actually classifies the work week as 40 hours for overtime purposes, yet here in Ontario its 44.
So there is certainly room to provide a better work-life balance as one part of a broader solution.
